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THE NERC MST RADAR FACILITY AT ABERYSTWYTH
MST RADAR DATA PRODUCTS VERSION NUMBERS
The latest MST radar products are version-3
These were introduced in November 2006. Since it will take some time to generate version-3 files for the entire observation archive, please contact the Facility Project Scientist if you cannot find files for the days you require.
Only limited support can be provided for MST radar data products derived from earlier versions of the signal processing (see below). Users are therefore strongly encouraged to make use of version-3 processed data wherever possible. This does not apply to the raw radar data (IQ and Doppler spectra), for which only version 0 data are available. Please contact the NERC MST Radar Facility Project Scientist if you are having difficulties finding the data products you need.
Although gradual changes have been made to the MST radar signal processing since the radar began operations in 1990, these changes have not been documented and the people responsible for them have now retired. Therefore all data stored in the original file formats have been retrospectively classified as version-0 products.
The signal processing makes use of a number of non-standard product definitions and simplifying assumptions, which were largely necessary in order to allow real-time processing using 1990-vintage computer technology. No explicit reliability flagging is used in these files, although the processing is robust and the data are typically good under suitable signal-to-noise conditions. The data products are spread across a number of different files, all of which use non-standard formats (both ASCII and binary) and for which only limited documentation exists. Follow the file format pages for further information.
The averaged data products represent 12 minute time averages (typically 3 - 5 cycles of observation). This can obscure small scale features such as turbulence and gravity waves. The ASCII versions of the 12 minute averaged files have not been produced since May 2004.
Version-1 data products are primarily available for the period June 2003 - December 2004. A key feature of the new products is the use of standard (NASA-Ames) format (ASCII) files. These make the data much easier to read and to understand. There are only 2 types of version-1 data products, both of which represent unaveraged data. The radial files are very similar to those from the version-0 (unaveraged) processing. The Cartesian files contain wind data, tropopause altitude and sharpness information and a number of radar return parameters (signal power,aspect, spectral width and beam-broadening corrected spectral width) on a regular grid. It is not necessary to know much about the way in which the radar operates in order to make use of the data from these files and they are recommended for most purposes. Follow the file format links for full details of the file contents.
The version-1 signal processing makes use of a time-continuity algorithm for reliability flagging. Initially the strongest signal within each Doppler spectrum is assumed to be the desired one, and the reliability flagging subsequently removes outlying data points. For the most part this has proved to be very effective, particularly in regions of low signal-to-noise ratio. This means that the maximum useful altitude for wind-profiling purposes (in the ST mode) is typically between 17 and 20 km, as opposed to between 15 and 17 km for the version-0 (unaveraged) processing. However, there are 3 known problems with the data:
Version-2 processing is essentially the same as that used for version-1. The only difference is that it makes use of the complementary beam horizontal velocity variability information (also available in version-1 files) to provide additional reliability flagging. This has proved to effective at removing data contaminated by the 3 problems noted above. This leads to more gaps in the data. Since Version-2 data products are also written in NASA-Ames format files, they can be read by routines written for version-1 products after making a few very small modifications. Version 2 data products are available for the entire observation archive until the end of 2006. New files will cease to be available when a new data acquisition system is installed in early 2007.
An improved, multiple-signal-component processing scheme has been under test, in collaboration with the Met Office, since January 2006. The quality of the thirty-minute-average wind-profile data is measurably better than that of v0 data and the Met Office switched over to v3 data for operational assimilation in September 2006. More details about the processing scheme, together with statistical measures of the wind-profile data quality, are available here.
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Last updated 9th November 2006